Epidemiological data on the relationship between endometriosis and diet have until now been scanty, said the Italian researchers, but their new results call for a prospective study to investigate further the possible links between diet and the condition.
Women with the highest fruit and veg intake were 40 per cent less likely to develop endometriosis, they report in today's issue of Human Reproduction (vol 19, no 8, pp1755-1759).
Endometriosis is a painful and distressing condition whereby endometrial tissue, which under normal circumstances is found only in the lining of the womb, develops outside the uterus and attaches itself to ligaments and organs in the abdominal cavity. This tissue responds to the menstrual cycle as though it were still inside the uterus. The repeated growth and disintegration of endometrial tissue in the abdomen can cause bleeding, pain, inflammation, adhesions and infertility.
The condition, estimated to affect up to five in every 100 women in Italy and probably in the rest of Europe, is therefore hormone-related and scientists are increasingly investigating diet's role in hormone-related disease. Diet has been shown to have a potential impact on ovarian and endometrial cancer.
The researchers used interviews and structured questionnaires to compare the medical and reproductive history, lifestyle and diet of over 500 women under the age of 65 with clinically confirmed endometriosis with a group of over 500 matched controls with no history of the disease.
Diet was assessed in the year leading up to the interview, based on how many times a week the women ate portions of selected dietary items, including the major sources of retinoids and carotenoids in the Italian diet, alcohol and coffee consumption. Then the researchers divided the intake into portions approximating to low, intermediate and high intake of the various dietary factors.
"What we found was that there was a 40 per cent relative reduction in risk of endometriosis in women with higher consumption of green vegetables and fresh fruit. But, for those with a high intake of beef, other red meat and ham, there was an increase of about 80-100 per cent in relative risk," said lead researcher Dr Fabio Parazzini from the Gynaecologic Clinic of the University of Milan.
With a prevalence of 5 per cent in Italy, the findings suggest that the occurrence of endometriosis could be cut to around 3-4 per cent, or about 200,000 fewer cases in Italy and probably 800,000 fewer prevalent cases in Europe, he added.
Hormonal factors are a potential link between diet and endometriosis, since the risk may be increased by exposure to unopposed oestrogens, and a diet rich in fat increases circulating unopposed oestrogens, suggested the researchers. The protective effect of a diet rich in green vegetables and fruits is more difficult to explain, they noted, but similar findings have been seen for the risk of breast and endometrial cancer, two hormone-related diseases.
There was no significant link between endometriosis and consumption of milk, liver, carrots, cheese, fish, wholegrain foods, coffee or alcohol and no association with butter, margarine or oil.
Dr Parazzini said there were some limitations in the study: the diet section was restricted to a few selected indicator foods and there was no estimate of portion size (therefore no estimate of the total intake in calories). However, since the possible relationship between diet and endometriosis was probably not known to the interviewers or the majority of women interviewed this was unlikely to have biased the results.
The association between vegetables, fruit and meat was unlikely to be due to chance because the researchers analysed several dietary items. However, it was possible there was a 'healthy woman' effect as a high intake of green vegetables, fruit and fish may be generally indicators of more health-conscious attitudes. Also, women who paid closer attention to their health may be more likely to have endometriosis diagnosed.
"However, despite these limitations, our study does suggest that there is some link between diet and risk of endometriosis and indicates that we now need a proper prospective interventional investigation to study these factors," concluded the researchers.